Ultrasound from a focused ultrasonic transducer can be used to selectively treat regions within the interior of the body. Ultrasonic waves are transmitted as high energy mechanical vibrations. These vibrations induce tissue heating as they are damped, and they can also lead to cavitation. Both tissue heating and cavitation can be used to destroy tissue in a clinical setting. However, heating tissue with ultrasound is easier to control than cavitation. Ultrasonic treatments can be used to ablate tissue and to kill regions of cancer cells selectively. This technique has been applied to the treatment of uterine fibroids, and has reduced the need for hysterectomy procedures. At lower powers or in pulsed mode, ultrasound can be used to selectively deliver genetic material or medicine to a region.
To perform ultrasonic therapy, a focused ultrasonic transducer can be used to focus the ultrasound on a particular treatment volume. The transducer is typically mounted within a medium, such as degassed water, that is able to transmit ultrasound. Actuators are then used to adjust the position of the ultrasonic transducer and thereby adjust the tissue region that is being treated.
The US-patent application US2004/0122323 shows a system for focusing ultrasonic energy through tissue and an imager for imaging the tissue region. Phase and amplitude correction factors are employed to focus the ultrasonic energy. The respective correction factors compensate for variations in the speed of sound of the tissue types within the tissue types. These correction factors are determined by analysing images and identifying tissue characteristics from the images.